The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The selection of battery materials includes considerations such as the desired power output for and any size limitations of the particular device incorporating the battery. With rechargeable batteries, capacity and rate capability or the rate at which the battery receives and delivers an electrical charge is also considered. In electric vehicles or other high-power applications, both the capacity and rate capability are the major priorities because of the extended range and high charge/discharge rates demanded by these applications.
With respect to lithium ion batteries, there is a loss of capacity and rate capability because after the initial charge—discharge cycles of new battery, there is an “initial cycle irreversibility” or a loss of 10 to 50% of available lithium ions. Thus, the initial cycle irreversibility decreases storage capacity of the battery for subsequent charges and discharges. To compensate for the initial cycle irreversibility and decrease in storage capacity, the battery size may be increased. As another option, alternate electrode systems may be used that modify the type of negative electrode in the system. However, these compensations and alternate electrode systems have shortcomings and provide technical barriers for commercialization of an optimized battery. In addition, there is an unacceptable rate of metal dissolution in some of the oxide positive electrodes, causing electrode degradation and limiting their applications for long term cycling.
Current lithium ion battery technology is based on low-energy-density carbonaceous or lithiated graphite negative electrodes and either oxide positive electrodes or phosphate positive electrodes. Current positive electrode materials are limited to less than one electron per transition metal, with maximum capacity between 100-200 Ah/kg in practical lithium cells. The oxide positive electrode also reacts with the electrolyte and generates oxygen at a high state of charge through an exothermic reaction, particularly at elevated temperatures, which causes an increase in cell impedance. The positive electrode decomposition impacts cell performance and may lead to battery thermal run-away. Additionally, transition metals like cobalt and nickel used in oxide positive electrodes significantly increase cost. Other options such as phosphate positive electrodes have an intrinsically large band gap and, therefore, require a specialized coating (with carbon) or doping that adds to the overall cost. In addition, most oxide cathodes suffer from dissolution of transition metals such as manganese, particularly at elevated temperatures that limits their applications.